The present invention relates to a pole structure in a permanent magnet type electric rotating machine, which is composed of a stator having a salient-pole concentrated winding, and a rotor having a permanent magnet arranged and fixed in a circumferential direction, and which is suitably used particularly for a hybrid electric vehicle. The invention further relates to a hybrid electric vehicle using such a permanent magnet type electric rotating machine.
Generally, as regards an electric rotating machine for an electric vehicle, a so-called vehicle wheel motor for an electric vehicle has been used as a driving source for an industrial vehicle such as a load carrier. For example, one disclosed in JP-A-8-99538 has already been known. Such a vehicle wheel motor includes a permanent magnet type electric rotating machine having a salient-pole concentrated winding. According to this technology, to suppress the generation of noise at an extremely low speed, a ratio between the number of magnetic poles for a rotor and the number of slots for a stator is set equal to a predetermined value. The above conventional technology provides an exemplary structure where the number of magnetic poles for the rotor is 8, and the number of slots for the stator is 12. However, such a technology is designed to suppress the generation of noise by performing so-called skewing magnetization in a surface magnet type electric rotating machine having a magnet disposed on the surface of the rotor. Although the fixing of the magnet to the rotor surface is not specified, it can be understood from its structure that the magnet is fixed by adhesive or the like.
For example as disclosed in JP-A-11-299199, a permanent magnet type electric rotating machine presented by the present inventors and an electric vehicle using such an electric rotating machine have been known. This electric rotating machine is different from the machine of the invention comprising a stator having a salient-pole concentrated winding in that a so-called distributed winding having three-phase 8 poles/48 slots (1:6) is set for a stator iron core. An angle xcex8 (mechanical angle) between the circumferential width of each permanent magnet in the outer peripheral surface of the stator side and the shaft center f the rotor is set at xcex8≈nxc3x97xcfx84s+16/P ( is a natural number), where a slot pitch of the stator is xcfx84s (mechanical angle, as shown in FIG. 1), and the number of poles is P.
In addition, as regards an electric motor for other than vehicle, for example as disclosed in JP-A-7-255138, there is available a permanent magnet type electric synchronous rotating machine structured to have the number of rotor poles set at 6, and the number of stator slots set at 9. However, this technology uses a magnet shaped like a convex lens in section, and a triangular groove for preventing the leakage of magnetic fluxes is provided between the poles.
In recent years, from the standpoint of protecting the global environment, so-called hybrid electric vehicles equipped with gasoline engines and electric motors have been presented in a part of efforts to reduce toxic exhaust from automobiles, and expectation is now placed on the practical use thereof. However, in the hybrid electric vehicle expected to have a structure where a general gasoline engine and an electric motor are directly connected to one and the same drive shaft (i.e., mounted in a narrow place in a car body), the following problems can be pointed out for the electric motor of the conventional technology.
That is, first, in the surface magnet type electric rotating machine of the conventional technology disclosed in the above-described JP-A-8-99538, a noise reduction (reductions in cogging torque and torque pulsation) is achieved by skewing the permanent magnet in an axial direction. However, the problem of holding the magnet in the surface magnet type electric rotating machine still remains to be solved. Specifically, in the case of the electric rotating machine driven to the speed of revolution of about 3000 rpm as described in the conventional technology, the permanent magnet located in the outer periphery of the rotor can be fixed by adhesive or the like. In the case of the hybrid electric vehicle, however, the electric rotating machine and an engine are connected in series to the drive shaft. Thus, if the electric rotating machine is rotary-driven at the same speed of revolution as that for the engine (e.g., 6000 rpm), the holding of the magnet must be assured even during rotation at such a high speed. In this case, the magnet is bound by a non-magnetic material (e.g., stainless or reinforced plastic material). Consequently, a gap with the stator may be increased, and the size of the electric rotating machine itself may also be increased, leading to high manufacturing costs.
In addition, in the surface magnet type electric rotating machine having a magnet rotor like that of the conventional technology, in particular when a frequency becomes high during rotation at a high speed, an eddy-current loss may occur on the surface of the magnet.
Secondly, in the electric rotating machine designed to drive the vehicle, which is disclosed in the above-described JP-A-11-299199, as large output torque is required, a distributed winding having tree-phase 8 poles/48 slots (1:6) is set for its stator iron core. Consequently, the axial length of the electric rotating machine is longer. Therefore, this structure of the electric rotating machine is not suitable for the hybrid electric vehicle.
Thirdly, in the permanent magnet type electric synchronous rotating machine made widely known by the above-described JP-A-7-255138, a magnetic flux formed by the permanent magnet is caused to be a sine wave by the magnet shaped like a convex lens in section and the triangular groove provided between the poles to prevent the leakage of magnetic fluxes. Cogging torque is thereby reduced. However, the magnet shaped like a convex lens in section is costly. In addition, because of the triangular groove provided between the poles to prevent the leakage of magnetic fluxes, a mechanical strength of the rotor may be reduced. Therefore, this structure is not suitable for an electric rotating machine requiring a large output to be used for the hybrid electric vehicle.
The present invention was made to solve the problems described above in detail, which are inherent in the conventional technologies. An object of the invention is to provide a permanent magnet type electric rotating machine, and another object is to provide a hybrid electric vehicle using the same.
In order to achieve the foregoing object, in accordance with an aspect of the invention, there is provided a permanent magnet type electric rotating machine, comprising a stator having a salient-pole concentrated winding, and a rotor disposed by keeping a rotational gap with the stator, and having a plurality of permanent magnets arranged and fixed in a circumferential direction inside a rotor iron core and an auxiliary salient pole between the permanent magnets. In this case, a ratio between the number of poles for the rotor and the number of slots for the stator is 2:3 and, when a slot pitch of the stator is xcfx84s (electrical angle), an angle xcex8 (electrical angle) made by a circumferential width of the permanent magnet in the surface of the stator side with an axis of the rotor is set at xcex8≈nxc3x97xcfx84s/2+8xc3x97m (n=1 or 2, and m=1, 2 or 3).
According to the permanent magnet type electric rotating machine of the invention constructed in the foregoing manner, an axial length is short from the stator structure of a salient-pole concentrated winding shape, and thus the electric rotating machine can be mounted relatively easily even in a very narrow space inside the car body of the hybrid electric vehicle. In addition, by setting the peripheral length of the permanent magnet in the surface of the stator side, without any skewing with a molding magnet, torque pulsation and cogging torque can be reduced, or an induced voltage can be a sine wave.
In accordance with another aspect of the invention, there is provided a hybrid electric vehicle, comprising the above-described permanent magnet type electric rotating machine, which is mounted in serial connection to a drive shaft of an engine.
In the hybrid electric vehicle comprising the permanent magnet type electric rotating machine of the invention mounted thereon, vibration is reduced at the time of starting or stopping the hybrid electric vehicle. Thus, more comfortable riding can be realized.